﻿using System.Collections.Generic;

/// <summary>
/// The IPriorityQueue interface.  This is mainly here for purists, and in case I decide to add more implementations later.
/// For speed purposes, it is actually recommended that you *don't* access the priority queue through this interface, since the JIT can
/// (theoretically?) optimize method calls from concrete-types slightly better.
/// </summary>
public interface IPriorityQueue<T> : IEnumerable<T>
{
    /// <summary>
    /// Enqueue a node to the priority queue.  Lower values are placed in front. Ties are broken by first-in-first-out.
    /// See implementation for how duplicates are handled.
    /// </summary>
    void Enqueue(T node, double priority);

    /// <summary>
    /// Removes the head of the queue (node with minimum priority; ties are broken by order of insertion), and returns it.
    /// </summary>
    T Dequeue();

    /// <summary>
    /// Removes every node from the queue.
    /// </summary>
    void Clear();

    /// <summary>
    /// Returns whether the given node is in the queue.
    /// </summary>
    bool Contains(T node);

    /// <summary>
    /// Removes a node from the queue.  The node does not need to be the head of the queue.  
    /// </summary>
    void Remove(T node);

    /// <summary>
    /// Call this method to change the priority of a node.  
    /// </summary>
    void UpdatePriority(T node, double priority);

    /// <summary>
    /// Returns the head of the queue, without removing it (use Dequeue() for that).
    /// </summary>
    T First { get; }

    /// <summary>
    /// Returns the number of nodes in the queue.
    /// </summary>
    int Count { get; }
}
